The invention relates to a coolable infrared radiator element of quartz glass with at least one heating tube, which has a gas-tight current lead-through at each of its two ends. A long, stretched-out heating conductor is provided in the heating tube to serve as the radiation source. At least one cooling element is provided which has at least one cooling channel for a liquid coolant and there is a metallic reflector with at least one reflective surface at least in the area of the heating conductor.
These types of infrared radiator elements are known from DE 2,637,338 C3. An infrared radiator element is disclosed here, which has a water-cooled twin tube of quartz glass comprising a heating tube and a cooling tube, where a reflective layer of gold is provided on a surface of the cooling tube. The reflective layer is applied either to the outside surface of the cooling tube or to the surface of the shared wall surface of the heating tube and the cooling tube facing away from the heating conductor. The energy concentration allowed for this radiator is 400 kW/m2.
DD 257,200 A1 describes a high-power infrared radiation source, which has a long, stretched-out incandescent radiator in an envelope. The envelope is mounted inside a protective tube and offset by 3-15% relative to the protective tube in the plane of the radiation emission direction. A liquid cooling and filtering medium flows through the protective tube. On the surface facing the liquid medium, the envelope has several strips in the form of segments of a cylinder to serve as reflective surfaces. In contrast, the protective tube has a reflective layer in the approximate form of a half shell on the surface facing away from the liquid medium. To achieve maximum radiation output in the forward direction, three cylindrical segments are provided as reflective surfaces on the envelope; the distance between two cylinder segments is equal to the width of one of the segments, and one cylinder segment is parallel to the reflective surface on the protective tube.
EP 0,163,348 describes an infrared lamp with a coiled tungsten heating conductor in a quartz container. The quartz container is filled with a halogen gas to allow the halogen cycle to proceed. An infrared light-reflecting coating of gold or rhodium in the form of a half shell covers the surface of the quartz glass container, preferably extending over its entire length. Gas-tight current lead-throughs are provided in the quartz container in the form of thin pieces of molybdenum foil with electrical leads, pinched into the ends of the container.
DE 2,803,122 C2, finally, discloses a halogen incandescent filament lamp with a bromine cycle, where the lamp consists of a glass bulb of quartz glass, a filling gas, and a coiled tungsten filament. A metal bromide, which is introduced into the glass bulb in solid form, decomposes when the lamp is in the operating state; the bromine thus becomes available for the known tungsten-halogen cycle. Copper bromide is used here as the metal bromide.
The object of the present invention is to provide an infrared radiation source by means of which high energy concentrations of  greater than 500 kW/m2 can be achieved in conjunction with relatively minor radiation losses.
The task is accomplished in that at least one reflective surface, when viewed in cross section, describes a line around a surface, the opening for the passage of at least some of the liquid coolant being provided in the area of this surface. xe2x80x9cCross sectionxe2x80x9d means here a section perpendicular to the longitudinal axis of the heating tube, in which view the reflective surface can be seen only as a line. One of these lines should now, in cross section, enclose a surface. The line in this case is preferably a line which forms a circle, but other types of lines can also be used without difficulty such as lines which form a square, a rectangular, a triangular, an elliptical, a crescent-shaped, or other type of regular or irregular surface. Accordingly, at least one of the reflective surfaces recognizable in cross section forms a channel for the liquid coolant or least for a portion of it.
With this geometric design, it is possible to build a high-output infrared radiator with low radiation losses and energy concentrations of 1 MW/m2. The heating tube must be designed in this case for a specific output of up to 190 W/cm, for which very high heating conductor temperatures in the range of approximately 3,000xc2x0 K are required. At these high heating conductor temperatures, however, the stability of the quartz glass heating tube is at risk, while at the same time there is also a high probability that the cooling water will overheat or boil and thus that the radiator element will break. The stability of the quartz glass heating tube is achieved according to the invention by the use of a liquid coolant with a high heat absorption capacity, especially water in this case, to cool the tube. At the same time, the design of the reflector according to the invention prevents the coolant from heating up too much. Such overheating would happen if, for example, the reflective layer were to be provided on the external surface of a cooling tube, as already known according to the state of the art.
Now, however, there are different ways in which the special reflective surface can be provided.
For example, the reflector can consist of a layer of metal. The cooling element in this case can be a cooling tube with at least one cooling channel directly adjacent to the minimum of one heating tube, and at least one cooling channel is lined with the layer of metal. Gold coating on the inside surface of the cooling tube is preferably used here as the metal layer.
The reflector, however, can also consist of a thin-walled metal part. In this case, the cooling element consists of a cooling tube with at least one cooling channel directly adjacent to the minimum of one heating tube, and the cooling channel is lined with the metal part. The metal part can consist of a piece of foil or sheet metal. Foil, however, is more flexible and can be fitted more precisely to the internal dimensions of the cooling tube.
It is also possible for the reflector to consist of a thin-walled metal part, for the cooling element to be a cooling tube enclosing at least one heating tube, and for the thin-walled metal part to be mounted inside the cooling tube. A self-supporting reflector with a hollow structure can be preferably installed in the cooling tube, but also a combination of reflective layers on the cooling and/or heating tubes and a metal part can also be used.
A special embodiment involves a radiator in which the cooling element is designed as a metallic reflector. This means that a single component provides both the cooling property and the reflective property. As a result of the radiation impermeability of the reflector, this component should not enclose more than 50% of the circumference of the outer wall of the minimum of one heating tube. The reflector can have at least two cooling channels to transport the coolant.
It has been found effective for the heating conductor to be made of tungsten and for the heating tube to be filled with an inert gas doped with a halogen. Because a great deal of tungsten vaporizes at the high temperatures of a heating conductor, it must be doped with a halogen, preferably with ammonium bromide or copper bromide, so that a halogen cycle will go into effect. To prevent the ammonium bromide or copper bromide from condensing in the area of the electrical lead-throughs, an electrical connecting lead is provided between the heating conductor and the gas-tight current lead-throughs. The diameter of the connecting lead is selected so that the connecting lead heats to a temperature of 600-800xc2x0 C. at a rated current as a result of its electrical resistance.
A heating conductor in the form of a carbon ribbon can also be used in place of a tungsten heating conductor. In this case, the heating tube is either filled with a noble gas or evacuated. The carbon ribbon can be stretched by a spring or coiled.
Especially preferred is an infrared radiator element which has a first and a second heating tube, where some of the wall surface of the first heating tube serves simultaneously as a wall surface of the second heating tube.
So that specially shaped parts or spaces can be heated up or kept heated with the infrared radiator element, the heating tube and the cooling element can be curved.
As a result of this curvature, the two gas-tight lead-throughs of the heating tube can point in the same direction and be set up parallel to each other. As a result, it is possible, for example, for the electrical connections for the infrared radiator element to be located on only one side of the furnace space. To ensure the stability of the quartz glass heating tube, the heating tube is also designed preferably with an inside diameter of 10-17 mm. In this regard, the ratio of the coil diameter of the coiled heating conductor to the inside diameter of the heating tube should be at least 1:3.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.